The reference implementation is based on Ubuntu Touch, and use libhybris to get hw support. However, it's different from UT, by the fact that it's not using Mir, but Wayland directly through Kwin.
It seems to run Ubuntu Touch applications, X11 applications, KDE/QML ones and Jolla/Sailfish/Nemo ones. They seem to have Android apps on the roadmap too.
Except the drivers (through libhybris), everything is open source and numerous KDE/QML apps can run without modifications. It can also run without libhybris if you have kernel DRM.
The distribution is based on Kubuntu, and so far it works only on the Nexus 5.